Question from the Elasticsearch test

POST /_search
{
  "aggs": {
    "genres": {
      "terms": { "field": "country" },
      “aggs”: { 
          “avg_age”: { “avg”: { “field”: “age” }}
      }
    }
  }
}

POST /_search
{
  "aggs": {
    "genres": {
      "filter": { "field": "country" },
      “aggs”: { 
          “avg_age”: { “avg”: { “field”: “age” }}
      }
    }
  }
}

POST /_search
{
  "aggs": {
    "genres": {
      "terms": { "field": "country" },
       “avg_age”: { “avg”: { “field”: “age” }}
    }
  }
}

POST /_search
{
  "aggs": {
    "genres": {
      "terms": { "field": "country" },
      “sub_aggs”: { 
          “avg_age”: { “avg”: { “field”: “age” }}
      }
    }
  }
}